Polymer coatings are provided on objects having low electrical conductivity such as ceramics and glass for a variety of reasons such as for weight savings, shatter protection, aesthetics and touch. In particular, providing shatter protection to glass bottles containing carbonated beverages is of particular importance where the glass bottles are defective or mishandled.
Polymeric coatings can be applied by various means. The objects to be coated can be dipped into a polymeric melt or can be dipped into a fluidised bed of polymer powder particles. It is also known to coat objects using an electrostatic powder spraying process; c.f. DE 2424220, DE 2750370 C2 and DE 2750372 C2.
DE 2750370 C2 and DE 2750372 C2 disclose electrostatic spray coating processes in which the substrate (a glass bottle) is maintained at a temperature below the melting point of the polymer, and the powder is applied by way of silent discharge. Afterwards, the bottle is heated to melt the powder to form a coating, which is subsequently cured. These processes, however, require high investment costs, can lead to corrosion of the equipment as they require continuous discharge, have limitations to the speed at which they can be carried out, require the use of very fine polymer powder which is expensive to produce, often produce non-uniform coatings due to local discharges at the bottle surface, and can be dangerous to carry out due to shattering of the bottles during heating and quenching steps.
These disadvantages are overcome by the current invention.